The invention relates to an electrical heating element with a heat conductor in the form of meander-shaped windings, with the individual windings being mounted in openings in at least one insulating plate divided by solid parts.
Eleectrical heating elements of this kind have been proposed in, for example, German Patent No. 11 85 743, German Patent No. 14 40 381, German Patent No. 14 40 404, and German Patent No. 12 74 760. Moreover, U-shaped, bent, sheet metal strips used as reinforcing rails have been proposed in, for example, German Patent No. 12 58 523 and German No. OS 31 41 828; however, at best, the strips described in those patents provide a reinforcement in one direction and cannot simply be used as return conductors. The use of a sheet metal strip as a return conductor in order to mount both terminals of a heating element for bread toasters on one side is proposed in German Patent No. 16 15 253.
The goal of the invention is to provide a heating element of the aforementioned, especially one with considerable length and limited width, with increased stability, in a manner which is simpler and more advantageous from the manufacturing standpoint.
According to the invention, this goal is achieved in an electrical heating element with a heat conductor in the form of meander-shaped windings, with the individual windings being mounted in openings in at least one insulating plate separated by solid parts. By virtue of the fact that a one-piece retaining rail is provided and extends over the entire width of the insulating plates and essentially over their entire length, and has tabs on the side edges of the insulating plates, which are bent over on both sides of the plates and grip them, it is possible to realize a stiffening of the support in two directions.
In accordance with one embodiment, provision is made for terminals for connecting electrical connectors at one end, and the heat conductors are electrically connected at the other end with the rail. Another embodiment provides for the rail to have openings and solid parts on the side facing away from the tabs. By virtue of this construction, in particular the different thermal expansion behavior of the insulating plates and the retaining rails is compensated for in a simple and optimal fashion so that no bending of the heating element, especially of the winding supports, occurs which could cause the ends of the windings to touch one another, producing a short circuit and hence a decrease in the resistance of the entire heat conductor and consequently damage to the latter. This is reliably prevented by the construction outlined above.
By virtue of the invention, a narrow, elongated, highly stable heating element is provided which is simple to manufacture. If the retaining rail is made of metallic material and is used as a return conductor, its terminal can be fastened firmly to it by eyelets or, in an extremely preferred embodiment, can be made integral with the retaining rail. The electrical connection between the heat conductor at the end which is opposite the terminal end is preferably accomplished by an eye, thus producing a reliable mechanical and electrical contact at this point.
While temperature switches (regulators and monitors) were formerly provided in heating elements of the aforementioned type, they had to be mounted in advance at a specified location. This specified location could not take into account the different installation conditions and hence different temperature conditions prevailing in different units, so that separate heating elements sometimes had to be provided for different units and had to be inventoried, or problems could arise, depending on the unit, such that the temperature switch would not respond under the desired temperature conditions.
Therefore, according to the invention, a temperature switch is displaceably mounted on the retaining rail, and, in particular, the retaining rail is gripped by the tabs of a retainer for a temperature switch. The use of continuous retaining rails makes it possible for the temperature switch to be secured to them to prevent its falling off or being removed, but permits it to be displaceably mounted tomove along the rail or rails. As a result, the complete heating element can be manufactured with the appropriate temperature switch and can be stored with a finisher who then, depending on the installation conditions, can slide the temperature switch along the rail to a desired location where it is either held positively or can be additionally mounted in such a way that it will not come loose, for example, by riveting or welding it to the rail. If the rail is made of side tabs connected by solid parts, an additional design provides for the temperature switch to be held in place on the retaining rail by the solid parts on the latter. The rail can also be used as a conductor for the current supplied through the temperature switch, so that the rail, by virtue of the holder for the temperature switch, provides a contact between the switch and an electrical connection. The other contact of the switch must be insulated from the switch mount and provided with a separate connecting element for connection of a cable.